WotC's posted a pdf of the rules primer they're handing out at the D&D experience.
Some of the big reveals (several of which I also posted on Nifty):
1. We have the official list of classes. Here they are, categorized by role:
Controller - Wizard
Defender - Fighter, Paladin
Leader - Cleric, Warlord
Striker - Ranger, Rogue, Warlock
Apparently, until and unless supplements add more controllers, every party has to have a wizard.
2. Yep, you're supposed to use at will powers way more often than standard attacks.
3. What's that about fewer die rolls? If you use an attack that affects multiple targets, you have to make an attack roll for every target, though you only make one damage roll.
4. It looks like there are almost as many actions in 4e as in 3.5 (though I can't be sure, since I didn't collect all the 3.5 supplements). And you get 3 actions per round: 1 standard, 1 move, and 1 minor. Minor actions are not free actions; they're things like drawing/sheathing a weapon or opening a door.
You can use a minor or move action as a standard action, and you can use a minor action as a move action. Got that straight? I didn't think so. Yep, this stuff just got more complicated. The good news is that you can sheath a weapon, draw another one, and attack in the same round.
5. You can get a healing surge by taking a standard action called ""second wind," which also gives you a +2 to your defenses until your next turn. Apparently, this replaces Refocus as the action to take when you've got nothing else to do. Clerical healing powers apparently also heal you by your surge value and cost you one of your daily surges. Don't ask me why.
6. Per encounter powers refresh after 5 minutes, the duration of a "short rest" in 4e. I'm not sure what happens to the bookkeeping if the PCs don't take a short rest after every encounter.
7. Frank will be really happy about this one. They've explicitly defined the length of a day in 4e (for purposes of refreshing per day powers and healing surges), and it's even shorter than Frank's 4e day. You only need to rest for 6 hours.
8. You start out with 1 action point and get one more for every 2 encounters you live through until the end of the "day," when your action points are reset to 1. This sounds like a lot of bookkeeping.
9. No more keeping track of rounds. Everything that doesn't have a 1-round duration either uses the new saving-throw mechanic (which is officially confirmed, BTW) or lasts until the end of the encounter.
10. Reach only works on attacks, so you don't have to worry about provoking AoOs from opponents 2 squares away on your move, unless they have a special power called "threatening reach."
11. It's official that only rogues (unless some other class gets that special feature) can catch their opponents flat-footed at the beginning of combat.
12. Cover gives a static -2 penalty to attacks, even if it's 100%. WTF?
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